Electrographic liquid developing apparatus



April 1, 1969 N. R. NAIL ELECTROGRAPHIC LIQUID DEVELOPING APPARATUS Filed June 30, 1965 NELSON R- NAIL INVENTOR. BY %M AT TO RNE YS United States Patent 3,435,802 ELECTROGRAPHIC LIQUID DEVELOPING APlARATUS Nelson R. Nail, Rochester, N.Y., assignor t0 Eastman Kodak Company, Rochester, N.Y., a corporation of New .lersey Filed June 30, 1965, Ser. No. 468,210 Int. Cl. Bb 5/02 U.S. Cl. ll3637 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to electrography and more particularly to a method and apparatus for developing electrographically produced latent images with liquid developers.

The term electrography is used herein to include (1) xerography, wherein an electrostatic image is produced on a photoconductive insulating layer, (2) Xeroprinting, wherein an electrostatic image is produced on an insulating layer, and (3) photoconductography, wherein a photoconductivity image is produced in a photoconductive layer. However, the present invention is useful in developing or making visible electrostatic images and conductivity images regardless of the method by which they are produced. Electrostatic images can be developed, for example, by cascade development, powder cloud development, magnetic brush development, or liquid development. Conductivity images are developed by passing an electric current through 'an electrolytic solution containing developer material in contact with the image-bearing surface whereby developer material plates out in the image areas.

The so-called liquid developing process in xerography employs liquid compositions comprising finely divided developer particles dispersed or suspended in an electrically insulating liquid medium or vehicle. The developer particles acquire an electrostatic charge which enables them to be attracted to the electrostatic image. Liquid development has the advantages of greater simplicity, greater speed of operation, improved control and versatility, and with certain developers, of eliminating the fixing step.

According to known xerographic liquid developing methods, an insulating record member bearing an electrostatic image is either totally immersed in a tank of liquid developer or is moved over a rotating toning roller which is partially immersed in 'a tank of liquid developer. The first method has the disadvantage of wetting both sides of the record member and the second method has the disadvantage, due to the high velocity of liquid needed and the great shearing force between the liquid and the image-bearing surface, of causing background and smearing of the image.

It is an object of the present invention to provide a system for developing electrographically produced latent images with liquid developers which is simple, fast, compact, and which provides a certain degree of flexibility.

It is another object of the invention to provide an apparatus which can be used to develop both electrostatic and conductivity images.

3,435,802 Patented Apr. 1, 1969 It is another object of the invention to provide a liquid deevloping process and apparatus which does not wet the back of the image-bearing record member and which does not cause background or smearing of the developed image.

It is another object of this invention to provide a liquid developing process and apparatus in which the liquid developer is applied only to the image-bearing side of the record member and in which the liquid developer does not impinge upon said side of the record medium at a high speed.

It is a further object of this invention to provide an apparatus for developing electrostatic images in which one element thereof is conveniently positioned for use as a development electrode whereby the effects of a development electrode may be employed without any reconstruction of the device and without losing any of the efliciency of the device.

It is a still further object of the invention to provide a liquid developing process and apparatus in which the liquid developer which is in contact with the image-bearing record member is constantly and automatically replaced with fresh developer.

The foregoing objects and advantages are attained by the present invention as follows. The record member to be developed is positioned horizontally with the latent image-bearing surface facing down. A pump, supplied from a tank of suitable liquid developer, directs a flow of liquid developer up through an outlet duct toward said surface. The open end of said duct is positioned adjacent said surface and is covered with a fine mesh screen whereby a welling up, or mound of liquid developer is produced in contact with said surface. The screen acts to arrest, slow down, or break the strong current of liquid developer and to soften its action upon the image-bearing surface. The screen may be used as a development electrode and may be biased by connecting it to any desired electric potential. In such case the screen is made of conductive material, such as stainless steel. The area of the mound of liquid developer can be made the same size as that of the latent image or it can be smaller, in which case relative movement between the record member and the mound of liquid developer is necessary for development of the entire latent image. The liquid developer is preferably returned from the mound to the supply tank by positioning the open end of the outlet duct above the open top of the liquid developer tank. The apparatus preferably includes a backing plate positioned behind the record member at the developing station. This plate aids in keeping the record member flat and uniformly spaced from and parallel to the fine mesh screen which covers the open end of the outlet duct. By making this backing plate conductive and connecting a voltage source between the backing plate and the fine mesh screen the apparatus can be used to develop a conductivity image in a record member. Thus the apparatus of the present invention can be used to develop either electrostatic images or conductivity images.

These and other objects of the present invention will be more fully understood by reference to the following detailed description when read in connection with the accompanying drawing, in which:

The figure is a cross-sectional view through the preferred embodiment of the present invention.

The figure shows an image-bearing record member 2 having an electrographically produced latent image on a surface 4 thereof. The member 2 is moved through the liquid developing station of the present invention by means, for example, of two sets of rollers 6 and 8. A pump 10 having an inlet duct 12 and an outlet duct 14- is mounted by any suitable means (not shown) within a tank 16 containing a quantity of suitable liquid developer 18. The pump can be a centrifugal-type pump in which the rotor is connected to a motor 20 through one wall of the tank 16. The discharge end of the outlet duct 14 is covered with a piece of fine mesh stainless steel screen 22. The screen 22 can be connected to a suitable voltage source 24 -by means of a switch 26, if desired. The screen 22 breaks the flow of liquid developer toward the imagebearing surface 4 and softens the action of the liquid developer thereon. A Welling up or mound 28 of liquid developer is produced in contact with the imagebearing surface 4. A backing plate 30 is provided behind the record member 2 and in contact therewith. The plate 30 ensures that the record member 2 will be flat and uniformly spaced from the screen 22 at the developing station. The plate 30 (or alternatively the conductive layer, if there is one, in the member 2) can be connected to a voltage source 32 by means of a switch 34 when the apparatus is to be used to develop photoconductographic prints.

Photoconductography is a well-known electrographic system and is shown, for example, in US. Patents 3,106,155, 3,057,788 and 3,010,883. When the apparatus shown in the figure is used to develop a conductivity image the switch 26 is open and the switch 34 is closed. Any of the known photoconductographic liquid developers may be used in this process. Provision may be made for grounding the backing plate 30 if desired. Further, the screen 22 may be insulated from the outlet duct 14 and pump 10 but this is not necessary. As is well-known in the art the bias potential from the voltage source 24 may be applied either to the screen 22 or to the plate 30.

A squirrel cage made from a small blower fan or motor together with its housing was mounted within a liquid developer tank and connected to a variable speed motor through waterproof bearings in one wall of the tank. The open end of the outlet duct of the housing was covered with a piece of fine mesh stainless steel screen. The tank was filled with liquid developer to within /2" from the top of the tank and the motor was started.

A xerographic coating comprising zinc oxide and a 50/50 copolymer of n-butylmethacrylate and isobutyl methacrylate (for example, Lucite 46, manufactured by E. I. du Pont de Nemours and Co.) was conventionally charged and exposed and then developed in the above described apparatus using a self-fixing xerographic liquid developer. The xerographic plate transport speed was 1.5 inches per second. Very satisfactory, smudge-resistant, good-quality prints were obtained by this method.

Various alternatives to the above described embodi- 4 of, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinbefore and as defined in the appended claims.

I claim: j 1. Apparatus for developing an electrographic latent image on an image-bearing surface of a record member with a liquid developer comprising:

support means for positioning said member at a developing station with said image-bearing surface facing downwardly, a tank for containing a quantity of liquid developer, a pump positioned inside said tank and below the liquid level for providing a flow of liquid developer from said tank, said pump having an inlet below the liquid level and an 'open ended outlet that extends above the liquid level, 5 said open ended outlet positioned in closely spaced relation to said image bearing surface at the developing station for directing said flow of liquid developer toward and at substantially a right angle to said image bearing surface, and flow arresting means covering said open ended outlet for restricting said flow of liquid developer so as to produced a mound of liquid developer between said open ended outlet and said image-bearing surface for contacting the latter. 2. The apparatus according to claim 1 in which: said record member is a photoconductographic record member, said electrographic image is a conductivity image, said flow arresting means comprises an electrically conductive fine mesh screen that covers the open end of said outlet and is arranged in spaced parallel relation to said surface, and including a backing electrode in contact with the surface of said member opposite said image-bearing surface at said developing station, and a voltage source connected between said backing electrode and said screen. 3'. The apparatus according to claim 1 in which said latent image is an electrostatic image, and said how arrestments are possible. Other flow arresting means may be employed in the present invention in place of a fine mesh stainless steel screen, such as a perforated plate or baflle means. Further, the pump need not be physically mounted within the tank but can be mounted outside of the tank. The only requirement is that the inlet duct be in liquid communication with the liquid developer in the tank. The mound of liquid developer need not be produced directly above the tank but can be produced above a tray separate from the tank having a return line to the tank. Since the apparatus shown in the figure can be used to develop either electrostatic or conductivity images, it may be desirable to provide two supply tanks, one containing a zerographic liquid developer and one containing a photoconductographic liquid developer, two inlet ducts, two return ducts from the tray, a valve for connecting the pump to the appropriate liquid developer tank and a valve for returning the liquid developer from the mound to the appropriate supply tank.

The present invention has been described in detail with particular reference to the preferred embodiments thereing means comprises a fine mesh screen.

4. The apparatus according to claim '3 in which said screen is electrically conductive and including means for applying an electrical bias potential to said screen.

References Cited UNITED STATES PATENTS 3,060,429 10/1962 Winston 117-93.4 X 3,068,115 12/ 1962 Gundlach 117--37 3,117,029 l/1964 Hines 11793.4 X 3,168,021 2/ 1965 Levene l1'8637 X 3,169,887 2/1965 York 1l8-637 3,192,897 7/1965 Young 11737 X 3,196,829 7/ 1965 Elliott et a1 118-410 X 3,198,170 8/1965 Onishi 1l793.4 X 3,203,395 8/1965 Liller 117-37 X 3,256,855 6/1966 Oliphant 118-637 3,327,948 6/1967 Gignoux 1l793.4 X 3,334,613 8/1967 Young 11 8-637 3,336,906 8/1967 Michalchik ll8-637 WILLIAM D. MARTIN, Primary Examiner.

EDWARD J. CABIC, Assistant Examiner.

US. Cl. X.-R. i 

